Snap, crackle, pop. I’m listening to a brain talking in a language that seems unintelligible, a chorus of millions of neurons firing, sounding to my ear like the electrical fuzz of a shortwave radio between stations. Then comes a distinctive “pop.” I hear it again: “pop.” I am watching a video. The brain in question belongs to a bearded man sitting in a chair. The victim of a stabbing three and a half years ago, he is paralyzed from the neck down. The ventilator that allows him to breathe is gurgling. Matthew Nagle, a 25-year-old former high-school football star from Weymouth, MA, has a round, titanium pedestal protruding half an inch from his head on the right side near the crown.

On July 4, 2001, Nagle became involved in a melee at Wessagussett Beach in Weymouth. He remembers only that fists began to fly and that a friend was under attack. Someone shouted something about a knife, and Nagle blacked out. Later that night, when his father, a police detective, got a call from the police, he was told that his son would probably die. The 20-centimeter blade had severed the spine in his neck, leaving him paralyzed and on a respirator. Nagle survived, but after years of immobility and tedium, he agreed to take part in a clinical trial to determine whether or not a human could safely manipulate a computer cursor using a brain-computer interface (BCI).

Attached to the pedestal, surgically implanted beneath Nagle’s skull, is an array of electrodes on a chip contiguous to the part of his brain that controls motor ac­tivity. The chip is the size of a baby aspirin: its 100 tiny hair-thin electrodes pick up the electrical signals transmitted by the brain, each electrode capturing signals from a few nearby neurons. As demonstrated in a video I watched late last year, a square, gray plug is screwed onto the pedestal; the plug is attached by wires to a nearby computer. When Nagle’s neurons fire, the impulses are read and decoded by software that can interpret the electrical pops of sets of neurons. The computer reads Nagle’s thoughts – or at least the pops recorded by the electrodes – and deciphers a few simple commands spoken in the electrical language of the brain.

Nagle sits in front of a prosthetic hand. Originally designed for amputees who would con­trol it by twitching muscles in the stumps of their arms, the robotic limb has been hooked up to the computer and will open and shut when Nagle imagines that he is opening and closing his own left hand. Nagle may be paralyzed, but the neurons in his cerebrum that control motor activity are quite healthy.

Snap, crackle, pop.

I hear a technician ask Nagle to imagine using his hand. He does. This fires up the relevant neurons in his motor cortex, creating an electrical signal that is received by the implanted electrodes and decoded by the computer – a series of events that causes the artificial thumb and forefinger to open and close.

The implications for Nagle and others like him, trapped inside malfunctioning bodies by injuries or degenerative neurological diseases, are wonderful. Nagle is the first human ever to operate a prosthetic arm with only his mind. During a visit to his room at an assisted-care fa­cility south of Boston, I further observed Nagle operate a cursor on a computer that allows him to send and receive e-mails, play simple games, and control his television. Surrounded by photographs of his friends and family, and by his veritable shrine to the Boston Red Sox and their 2004 victory in the World Series, Nagle worked with technician Maryam Saleh as she calibrated the computer to his brain. The setup is bulky, about the size of a washing machine, with two monitors for the technician and one for Nagle.

When I saw him, Nagle was tired and a bit cranky, his handling of the cursor rudimentary. He attempted to catch an animation of a small bag of money with the cursor. “I can’t get it today, not even close,” he complained.

Later, Saleh set up the computer so that Nagle could change channels on a television, and with effort Nagle was able to switch the channel. The presence of a reporter may have been part of the problem that day. The scientist chiefly responsible for Nagle’s device, neuroscientist John Donoghue of Brown University, assured me that his patient had done much better in the past. Nagle told me that the day before my visit, he had successfully manipulated a more advanced prosthetic arm with joints that enabled humanlike movements. “It worked really well,” says Nagle. “I could move it all around.”

“It’s encouraging that the system has worked this well,” says Leigh Hochberg, a Harvard University neurologist and an expert on patients with severe motor impairments. Hochberg is a principal investigator for the U.S. Food and Drug Administration trial approved in April of last year to test the implants on five patients. (So far, Nagle is the only volunteer for the trial.)

For now, the technology is very crude. The computer understands only a tiny fraction of what goes on in Nagle’s brain, where billions of neurons can be firing at any one time, with trillions of interactions. Still, the implant is a significant step, a neurological Rosetta stone in the most complex deciphering project in history, one that might not be completed for decades, if ever.